Pressure Measurement and the Flow System

Pressure Measurement and the Flow System.—For moderately precise g.l.c.-determinations of activity coefficients [as obtained from equation (3)], the outlet pressure is usually considered as being atmospheric pressure and can be measured on a normal Fortin barometer. The inlet pressure is usually determined by difference using a manometer placed in the carrier-gas flow line. An excellent review by Ambrose gives details of such pressure measurements. 

It is important to have no measurable fluctuations in inlet or outlet pressures or in the carrier-gas flow rate. For atmospheric pressure g.l.c. a two-stage 

For medium-high-pressure g.l.c. the problem is more difficult as both the inlet and outlet pressures must be controlled. The above types of regulating valves have proved satisfactory when used in conjunction with a fine-control 

At the higher pressures, leaks pose a serious problem. The system should be regularly checked for leaks, and the positioning of on-off valves in the line should be arranged so that parts of the apparatus can be isolated and tested. 

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